1. Field
This relates to implantable medical devices having external electrical connections and electrical feedthroughs, specifically to miniature implantable connectors for interconnection of implantable devices and associated lead wires.
2. Prior Art
In a typical implantable electronic device, such as a cochlear implant, heart pacemaker, or a brain-stimulating device, the device contains electronic circuitry (electronics) that resides in a hermetic housing or case. The device is attached to at least one electrical lead (“lead”) that has sensing and/or stimulating electrodes on its end distal from the device which are implanted in the tissue targeted for therapy (cochlea, heart muscle, particular area of brain, etc.). Other leads may connect the device to additional implantable system components, such as drug delivery devices, implantable inductive coils (for energy delivery to the device and/or data communication with the device), or power sources, which may have to reside in a more accessible body area for easier charging and/or replacement.
It is preferable that the implantable leads and devices be detachable so that either a device or leads can be implanted or explanted independently. This functionality is provided by a connector on the device's case, which disengageably connects the proximal (near-device) lead terminals to the device's electronics. The connector's contacts must connect with the device's electronics across a hermetic feedthrough so that the hermeticity of the device's case is not compromised, i.e., the electronics remains sealed from the body fluids and moisture. It is further desirable that the connector has a small size, can provide a rapid connection and disconnection without special tools, and allows multiple connect and disconnect cycles without loss of function.
In many existing devices the connector is implemented in a molded header (insulating housing), formed from a hard medical grade polymer on the edge of the device's case, and the connector's receptacle contacts are connected to the feedthrough pins by discrete wiring, which is subsequently overmolded (covered and sealed by insulating material). The wiring must interface two dissimilar and spatially separated contact patterns and can be quite intricate. The assembly and the associated molding and testing can be labor intensive, as discussed in U.S. Pat. No. 7,274,963 (2007) to Spadgenske.
The header connectors for iso-diametric (having constant diameter) leads typically have blind lead receiving lumens (i.e., the lumens are open at one end only) into which a lead is inserted with significant force (adequate to generate contact forces and compress the seals), so lead insertion force and contact registration can be an issue. The header connectors are therefore more suitable for larger-diameter, lower-contact-count leads, such as those used with cardiac rhythm management devices, which can tolerate significant insertion force and have more liberal contact registration tolerances.
U.S. Pat. No. 6,321,126 (2001) to Kuzma shows a header connector design for flat-lead terminals. This patent addresses the need for a high contact count, small-dimensioned connector, but this design is only applicable to leads with flat lead terminals and cannot be adapted to iso-diametric lead terminals. In addition, the contact system appears to rely on an elastomeric backing of the lead terminal body for providing contact pressure. Since elastomeric materials are prone to time-dependent permanent deformation, contact pressure may relax with time, especially because such connections have a low compliance (independent of the elastic backing, the contacts have limited elastic deflection reserve). The low compliance is also problematic when repeated mating is required.
As the implantable medical devices and systems become more capable and number of the leads and the lead contact count and density increase, there is a need for small but robust connectors to make reliable connections to devices or components of the implantable system. The small size is especially important for devices such as neural and cochlear stimulators which are implanted in the cranium, both for medical reasons (a smaller cranial cavity needs to be created) and for aesthetic advantages. In such cases, it may be desirable to build the connector interface directly into the device's feedthrough housing cavity so that receptacle contacts are co-located with the feedthrough pins.
My U.S. Pat. No. 6,662,035 (2003) shows a feedthrough-based connector design intended for a device implantable beneath the scalp. This patent teaches how to implement reliable direct metal-to-metal connections between lead contacts and the corresponding feedthrough pins. The illustrative dimensions of the two-lead connector are a depth of approximately 6.5 mm, a length of approximately 15.0 mm, and a breadth of approximately 13.0 mm. These dimensions are still excessive for locating the connector on an edge of the device case or for use in size-critical subcutaneous applications, such as inside the cranium. Unfortunately, the size of the above feedthrough-based connector cannot be radically reduced due to the following factors:
(a) The device uses compressible contacts located entirely above the exterior (outwardly facing) surface of the feedthrough dielectric substrate, on which an interposer (seal) is seated. The entire compressible contact must be accommodated within the interposer thus adding to the total connector height.
(b) The compressible contacts use C-shaped springs having significant width and height that cannot be traded to reduce connector size. For a given spring-loop length, required for adequate contact force and deflection, a smaller contact height will lead to a greater contact width.
(c) The contact width controls the width of the interposer seal, and thus the connector's overall width.
(d) The spring contacts are free-standing and thus are susceptible to intra-operative handling damage if made too fragile. A smaller contact must be made from a thinner material (and thus would be more fragile) or it will be too stiff and have a low deflection capability. It is important that the contacts have adequate contact compliance or deflection range in order to accommodate assembly tolerances and to assure an adequate deflection reserve for repeated mating.
(e) A robust spring contact (necessary for the handling integrity) and a wide seal require substantial clamping hardware, including a relatively large screw. This larger screw causes the feedthrough area between the leads to be poorly utilized.
Another issue in miniature implantable connectors is protection of the implantable leads from handling damage, especially during intra-operative attachment of the leads to a connector. In order to protect the miniature implantable leads, the lead terminals may need to be pre-inserted into a lead-receiving connector component without significant insertion force. Subsequent handling can easily cause the leads to inadvertently retract prior to connector pressurization, causing a loss of contact registration.